1. Technical Field
The present invention relates to a method of designing a progressive power lens.
2. Related Art
WO97/19382 describes a progressive multifocal lens that is used as a spectacle lens suitable for correction of presbyopia or the like. In this progressive multifocal lens, a progressive surface attached to the object-side surface is provided on the eyeball-side surface. Accordingly, since the object-side surface can be a spherical surface with a constant base curve, it becomes possible to suppress the variations in magnification due to a shape factor, to reduce the difference in magnification between a distance portion and a near portion, and to suppress the variations in magnification of a progressive portion. Therefore, it is possible to reduce image sway or distortion due to the difference in magnification, thereby providing a progressive multifocal lens that obtains a comfortable field of view. In the progressive multifocal lens described in WO97/19382, it becomes possible to combine the progressive surface and the toric surface for astigmatism correction on the eyeball-side surface using a combination expression, thereby reducing the image sway or distortion even in a progressive multifocal lens for astigmatism correction.
WO97/19383 describes a multifocal spectacle lens that has visual field portions being different in power, such as a distance portion and a near portion. In this multifocal spectacle lens, the difference between the average surface power of the distance portion and the average surface power of the near portion on the object-side surface is set to be numerically smaller than a predetermined addition power, and the average surface power of the distance portion and the average surface power of the near portion on the eyeball-side surface are adjusted, thereby providing a multifocal spectacle lens with the predetermined addition power. It becomes possible to adjust the average surface power of the object-side surface such that the difference in magnification between the distance portion and the near portion is reduced, and to reduce the difference in the average surface power of the object-side surface. Therefore, it is possible to provide a multifocal lens that has less sway or distortion of images due to the difference in magnification, and obtains a comfortable field of view with improved astigmatism, a wide range of distinct vision, less image sway, and the like.
JP-A-2003-344813 describes a double-sided aspheric progressive power lens that reduces the difference in magnification of images between a distance portion and a near portion, allows satisfactory vision correction with reference to a prescription value, and provides an effective wide field of view with less distortion when wearing. For that purpose, in JP-A-2003-344813, when the surface power in the horizontal direction and the surface power in the vertical direction at a distance power measurement position F1 in a first refractive surface on the object-side surface are respectively DHf and DVf, and the surface power in the horizontal direction and the surface power in the vertical direction at a near power measurement position N1 in the first refractive surface are respectively DHn and DVn, the relational expressions DHf+DHn<DVf+DVn and DHn<DVn are satisfied. The surface astigmatism components at the positions F1 and N1 on the first refractive surface are balanced with a second refractive surface on the eyeball-side surface, and the distance power and the addition power based on a prescription value are given with the combination of the first and second refractive surfaces.
JP-A-2004-004436 describes a progressive power lens that can reduce image distortion or blurring inherent in the progressive power lens and can improve wearability. For that purpose, in JP-A-2004-004436, a double-sided progressive lens with both the object-side surface and the eyeball-side surface being progressive surfaces is prepared, the surface addition power of the object-side surface is made negative, and the shape of the progressive surface is designed such that the average surface power distribution of the object-side surface and the eyeball-side surface are made similar.
JP-A-63-115129 describes a progressive multifocal lens which has a segment where power incrementally changes (continuously increases) from above to below substantially near the center of the lens in the horizontal direction. In this progressive multifocal lens, the area S of a region where astigmatism is equal to or smaller than 0.5 diopter is sorted into three regions A, B, and C of an upper portion from a distance eye-point of the lens, a portion from the distance eye-point to a near power measurement point, and a lower portion from the near power measurement point. If the suffix p is attached when the average power of the distance power of the lens is equal to or greater than +1.00 diopter, the suffix a is attached when the distance power is equal to or smaller than −1.00 diopter, and Sp=Ap+Bp+Cp and Sa=Aa+Ba+Ca are established, when the addition power of each lens is identical, the progressive multifocal lens has the astigmatism distribution of Ap>Aa and Cp<Ca or Bp+Cp<Ba+Ca.
JP-T-2006-506662 describes a double-sided progressive spectacle lens in which a progressive effect is distributed over the front surface and the rear surface of the progressive spectacle lens, and the ratio Q is explained by Q=Addvfl/AddGesamt. Addvfl represents an increase in surface power along a principal line on the front surface between a distance region and a near region, AddGesamt represents an increase in total power along the principal line between the distance region and the near region, and the ratio Q increases with expansion of a distance region effect F: dQ(F)/dF≧0.
There is a need for a progressive power lens for spectacles with less image sway or difference in magnification.